The present invention relates generally to an apparatus for controlled braking of a driven yarn engaging roll and, more particularly, to such an apparatus specifically adapted for controlled braking of independently driven rolls and a warp beam in a textile draw-warping system.
In virtually all systems involving the handling of a traveling yarn and similar strand-like materials by means of one or more driven guide rolls and/or a winding drum and the like, it is important when stoppage of the system becomes necessary that the rate of deceleration of the driven component or components be such as to not adversely affect the maintenance of some degree of uniformity in the tensioning of the yarn or other strand-like material. In many circumstances, it is necessary or highly desirable in such systems to effect stoppage of the traveling movement of the yarn or other strand-like material rapidly, e.g., when a breakage of the traveling material requires repair or when the driven components are operated at high speeds or otherwise have significant inertia, and accordingly it is common to brake the driven components to a standstill. Such factors are of particular concern in systems having plural independently driven components engaging the traveling yarn or strand-like material, especially if the driven components are operated at differing normal driven speeds or have differing inertial properties, which necessitate that the driven components be decelerated, whether by braking or otherwise, in synchronism with one another to avoid undesirable increases or decreases in the tension in the traveling yarn or strand material between the driven components.
For example, in a textile draw-warping system, a plurality of continuous synthetic filament yarns are fed in parallel side-by-side relationship through a drawing unit wherein the yarns are subjected to a drawing operation between spaced sets of drive rolls driven at differing speeds and subsequently the yarns are delivered to a warp beaming machine whereat the yarns are wound side-by side onto a warp beam. While the traveling speed of the yarns is desirably maintained substantially constant and, in turn, the respective driven speeds of the guide rolls in the drawing unit are likewise maintained substantially constant during normal operation, the driven axial speed of the warp beam must be progressively decreased over the course of the winding operation to maintain its peripheral surface speed, i.e. its yarn take-up speed, substantially constant as the progressive winding of the yarns about the warp beam gradually increases its effective diameter. As will also be understood, the overall mass of the warp beam and the attendant inertia thereof increases in relation to the increasing effective diameter of the beam. Accordingly, when stoppage of a draw-warping system is necessary, dramatic increases or decreases in the yarn tension are likely to result either or both between the differentially driven guide rolls in the drawing unit and between the downstream drawing unit guide rolls and the warp beam, which may result in yarn breakage or other yarn damage, unless the drawing unit guide rolls and the warp beam are stopped synchronously with one another.
Conventionally, compatible braking of the differentially driven drawing unit guide rolls and the warp beam is known to be accomplished in two possible manners. First, electrically-operated brakes may be applied to the driven components which are mechanically interconnected through a common gear box for synchronized braking, In another system, the respective drive motors for the driven components are braked dynamically in synchronism. While generally effective for their intended purpose, these conventional braking systems have several disadvantages. In the first type of braking system, the use of a gear train mechanically interconnecting the driven members undesirably increases the complexity and cost of the overall apparatus. With respect to dynamic braking systems, the maximum rate at which a drive motor can be braked dynamically is limited by the power rating of the motor and, thus, drive motors of relatively high power ratings must be utilized in order to achieve effective dynamic braking and, even so, the maximum practical operating speed of the draw-warping system is still limited by the dynamic braking ability of the drive motors utilized. Further, in typical dynamic braking systems, no means is provided for maintaining the braking rates of the individual drive motors in synchronism in the event undesirable deviations in braking occur.